Using a variety of molecular biological and biochemical techniques, structure/function relationships of several human immunodeficiency virus (HIV) genes have been examined. The role of the "A" (SOR) gene product during productive infection was evaluated by deleting a 620 bp segment from an infectious molecular clone of the HIV provirus. This alteration had no effect on viral gene expression or on the assembly or release of reverse transcriptase-containing virions in transfection experiments. However, a 1000-fold reduction in the infectivity of secreted particles was observed. This defect could be restored in transcomplementation experiments using an "A" gene cDNA clone. Efficient transfer of the "A" mutant was observed when virus producing cells were cocultivated with T4+ lymphocytes demonstrating the HIV has the capacity to spread "cell-to-cell" in addition to initiating exogenous infections as cell-free particles. To investigate the possibility that DNA viruses could augument gene expression of HIV, cotransfection experiments were conducted using the HIV long terminal repeat linked to the chloramphenicol acetyl transferase gene in the presence of DNAs from JCV, BKV, HSV-1, VZV, and bovine papillomavirus. Transactivation was observed with several of these unrelated viral DNAs suggesting that coinfection of cells by HIV and some of these agents could stimulate latent proviruses.